Methods and means for low temperature separation



Dec. 12, 1961 J. P. WALKER ETAL 3,012,629

METHODS AND MEANS F OR LOW TEMPERATURE SEPARATION Filed July 25, 1958 4Sheets-Sheet 1 N x k m l K: H d

INVENTORS Jay R Walker Robert W. Coggr'ns ATTORNEYS Dec. 12, 1961 J. P.WALKER ETAL 3,012,629

METHODS AND MEANS FOR LOW TEMPERATURE SEPARATION Filed July 25, 1958 4Sheets-$heet 2 Jay P. Walker Robert W Coggins ATTORNEYS Dec. 12, 1961 J.P. WALKER ETAL 3,012,629

METHODS AND MEANS FOR LOW TEMPERATURE SEPARATION Filed July 25, 1958 4Sheets-Sheet 3 INVENTORS Jay R Walker Robert 14 Coggins ATTORNEYS Dec.12, 1961 J. P. WALKER El'AL 3,012,629

METHODS AND MEANS FOR LOW TEMPERATURE SEPARATION Filed July 25, 1958 4Sheets-Sheet 4 Fig. 8

INVENTORS Jay R Walker Robert W Coggins ATTORNEYS nite States METHODS MENS FOR LOW TEMPER- ATUlRE SEPARATION Jay P. Walker and Robert W.Coggins, Tulsa, Okla, as-

signors to National Tank Company, Tulsa, Okla, a corporation of NevadaFiled July 25, 1958, Ser. No. 751,069 11 Claims. (Cl. 1S3-2.7)

This invention relates to new and useful improvements in methods andmeans for low temperature separation.

The invention is particularly directed toward the field of lowtemperature separation of distillate and water from relatively highpressure well streams of the type in which a considerable or a majorportion of the recoverable hydrocarbons may be present in the gaseousphase. Such recovery units normally involve a low temperature separationvessel into which the well stream is expanded through a choke, or otherpressure reducing means, for temperature reduction and condensation orliquefaction of the valuable light hydrocarbons, as well as theliquefaction of water which may be present in the vapor phase and whichmust be removed from the gaseous portion of the well stream prior tointroduction of the latter into a gas transmission pipe line.

Low temperature separation units customarily include means for heating aportion or all of the separated liquids in order to melt any ice or gashydrates which may be present, and it has been the practice to pass theincoming well stream through heating coils in the lower portion of thelow temperature separation unit for supplying the necessary heat. Such asystem often entails, however, the addition of heat to the well streamprior to its passage through the heating coils, and due to the heattransfer conditions which necessarily ensue, the well stream must beheated to temperatures well above those temperatures desired in theliquids in the lower portion of the low temperature separation unit.

Under some conditions, the well stream may need some degree of heatingprior to its passage through the choke or other pressure reduction meansin order to make certain that the well stream will be above the point ofgas hydrate formation prior to entering the choke so that all hydratesare formed downstream of the choke. When, however, the well stream isheated for the purpose of supplying heat to the lower portion of the lowtemperature separation unit, it is often necessary to heat the streamwell above that temperature necessary to ensure the absence of gashydrates prior to expansion of the well stream. Accordingly, the entiresystem is thus operated at a higher temperature than that required, andthe recovery of the desired portions of salable hydrocarbons isconsequently reduced or prevented.

It is also a common practice to supply heat constantly or at a constantrate to the lower portion of the low temperature separation unit, bothfor the reason that such continuous heating is often or usuallynecessary in order to melt all of the hydrates which may be formed, aswell as to overcome the inherent difliculties in achieving adequate heattransfer from a predominantly gaseous well stream to a body of liquidthrough heat exchange or heater coils. Here again, there is often awasteful heating of the well stream, large quantities of gas arerequired for continuously effecting such heating, and the well streamenters the choke at higher than necessary temperatures.

It is, therefore, one object of this invention to provide improvedmethods and means of low temperature separation in which the heat ofsteam is employed for heating the lower portion of the low temperatureseparation unit, both to obtain very effective heat transfer andutilization of the heat supplied through the steam, as

3,012,629 EC Patented Dec. 1 1961 well as to provide for whateverheating of the well stream may be necessary to prevent the formation ofgas hydrates upstream'of the pressure reducing choke and/or to controlthe composition of the gas leaving the low temperature unit.

A further object of the invention is to provide im proved methods andmeans for low temperature separation particularly adapted to utilizationwith well streams well as to ensure operation of the unit at the lowestpos-v sible temperatures in order that full'advantage may be taken ofwhatever pressure drops are available.

An additional object of the invention is to provide improved methods andmeans for low temperature separation particularly adapted to utilizationin instances in which it may be desired to vary the flowing volumes 0well streams rapidly over wide ranges.

Yet another object of the invention is to provide im-' proved methodsand means for low temperature separation wherein all necessary orrequired heating is carried out by steam which may be utilized atintervals or on a time-controlled basis so that the heating of the lowtemperature separation unit is not continuous but issupplied only atintervals and with high effectiveness to melt or decompose any gashydrates which may have accumulated in the low temperature separationunit, resulting in an overall operation of the low temperature unit atminimum temperatures for maximum dehydration of the well stream andmaximum hydrocarbon recovery.

An additional object of the invention is to provide improved methods andmeans for low temperature separation in which a source of steam isemployed on a controlled basis for supplying heat to the low temperatureseparation unit, and on a separately controlled basis for supplying heatto the incoming well stream prior to its passage through the pressurereducing choke for ,preventing the formation of gas hydrates upstream ofsaid choke and/ or to predeterrnine the hydrocarbon composition of thegas flowing from the unit.

Yet a further object of the invention is to provide improvai methods andmeans for low temperature separation wherein the incoming well streammay be heated to any necessary or desired degree to produce an outletgas of desired or selected hydrocarbon composition.

A further object of the invention is to provide improved low temperatureseparation means having steam heating coils in which the possibility offreezing of water in the coils, with consequent possible damage to orrupture of the coils, is avoided.

Other and more particular objects will be apparent from a reading of thefollowing specification and claims.

A construction designed to carry out the invention will be hereinafterdescribed, together with other features of the invention. I

The invention will be more readily understood from a reading of thefollowing specification and by reference to the accompanying drawings,wherein examples of the invention are shown, and wherein: t

FlG. 1 is a diagrammatic view illustrating a low tern peratureseparation unit constructed in accordance with this invention andadapted to carry out the methods hereof,

FIG. 2 is a schematic view showing the means for controlling theintermittent heating of the low temperature separator, I

FIG. 3 is a side elevational view illustrating the low temperatureseparator in greater detail,

FIG. 4 is a plan view of the unit shown in FIG. 3,

FIG. 5 is a vertical, transverse, sectional view taken upon the line 5-5of FIG. 3,

FIG. 6 is a vertical, longitudinal, sectional view of the lowtemperature separator,

FIG. 7 is a vertical, longitudinal, sectional view of the low pressuresteam generator, and

FIG. 8 is a diagrammatic view illustrating a still further modificationof the invention.

Turning now to FIG. 1 of the drawings, the numeral 10 designates a steamgeneration vessel of the type which may operate on automatic controlsunattended by operating personnel. A fire tube or other heating means 11extends into the vessel for supplying heat thereto, the fire tube havinga flue or vent 12 and being adapted for supplying heat to the interiorof the vessel 10 for the generation of steam, as an example steamsupplied under a pressure of the magnitude of pounds per square inch orunder higher or lower pressures. A well stream preheater 13 isassociated with the steam generator and encloses a set of preheat coils14 having a well stream inlet conductor 15 connected thereto and a wellstream outlet conductor 16 leading therefrom. A steam conductor 18 leadsfrom the upper portion of the steam generator 10 into the enclosure 13,and a condensate drain pipe 19 leads from the lower portion of theenclosure 13 through a check valve 20 into the lower portion of thesteam generator 10, or at least, a point below the normal operatingwater level therein. As pointed out hereinafter, suitable temperature orpressure control means may be incorporated in the steam supply conductor18 for controlling the degree of heating of the well stream in the coils14 in order that the well stream may be maintained at a level just abovethe point of gas hydrate formation prior to pressure reduction of thewell stream and/or in order that the composition of the gas leaving thelow temperature unit may be varied or controlled.

A low temperature separation unit 21 is associated with the steamgenerator 10, the low temperature separator desirably comprising anelongate horizontal vessel 22 into which the well stream conductor 16opens through a choke or other pressure reducing means 23 and a diverter24. A set of heating coils 25 is disposed in the lower portion of thevessel 22 with their lowest point above the steam generator 10 and hasconnected thereto a steam inlet conductor 26 leading from the upperportion of the, steam generator and a condensate return conductor 27connected into the lower portion of the steam generator through a checkvalve 28. A temperature controller 29 senses the heating of the lowerportion of the vessel 22 through a temperature bulb 30 and controls amotor valve 31 in the steam inlet conductor 26 for maintaining thedesired degree or level of heating within the vessel 22.

A gas outlet conductor 32 leads from the upper portion of the vessel 22through a back pressure valve 33 for withdrawing separated gas from thelow temperature separator, and a distillate or liquid hydrocarbonsoverflow sump 34 positioned near the end of the vessel 22 opposite theinlet diverter 24 is provided with a float 35 and a float control unit36 for operating a diaphragm valve 37 positioned in a distillate outletconductor 38 extending from the sump 34 to a low pressure separator 39.A water overflow sump 40 is provided in the vessel adjacent the sump 34and encloses a float 41 operating a control unit 42 which controls theopening and closing of a diaphragm valve 43 provided in a water outletconductor 44 extending from the lower portion of the sump 40. The lowtemperature separation unit 21 and the arrangements for removingseparated gas, hydrocarbons, and water therefrom, is shown and describedin detail in the US. patent to Jay P. Walker et al. No. 2,747,002.

The low pressure separator 39 is equipped with a floatoperated liquidlevel control 45 for operating a motor valve 46 provided in thehydrocarbon discharge conductor 47 leading from the lower portion of theseparator 39 to a point of hydrocarbon storage. There is also provided agas outlet conductor 48 leading from the separator 39 thrOugha suitableback pressure valve 49.

The steam generator 10 and low temperature separation unit 21 maydesirably be mounted upon a common base or platform 50, and thepreheater 13 may desirably be mounted upon the upper side of the steamgenerator 10. In this manner, a unitary and compact structure results,and much of the piping and other connections may be completed prior toactual installation of the unit at a producing well in the field.

In the operation of this form of the invention, the well stream, underhigh pressure, enters through the conductor 15 and passes through thepreheater coils 14 for elevation to a temperature sufiicient to avoidthe formation of gas hydrates in the well stream prior to the passagethereof through the choke 23, and/or to predetermine the temperature andhydrocarbon composition of the gas leaving the low temperatureseparator. Steam will be supplied to the preheater enclosure 13 throughthe conductor 18 in such quantities as necessary to carry out theaforesaid heating, and as the steam condenses in the course of suchheating, the condensates will be returned to the steam generator 10through the conductor 19 and check valve 20. The check valve, as isusual for this type of steam supply, prevents the reverse flow of fluidsthrough the conductor 19 from the steam generator to the preheaterenclosure. Of course, in some instances, the preheater 13 may beeliminated entirely, primarily when the well stream enters at such atemperature and pressure that heating thereof to prevent prematurehydrate formation is unnecessary and/or when control or variation in thecomposition of the exiting gas is not desired.

In passing through the choke 23, the well stream undergoes anappreciable pressure reduction and is therefore chilled to a quitemarked extent which causes the formation of ice and/or gas hydrates,along with the liquefaction of hydrocarbons and water. By this means,the gaseous portion of the well stream is sufiiciently denuded of waterand hydrocarbons as to permit its sale to a gas transmission pipe line,and at the same time, quantities of the valuable and salable liquidhydrocarbons are recovered. In the vessel 22, the hydrates and liquidportions of the well stream are separated from the gaseous portion,dehydrated gas being drawn olf through the outlet conductor 32 while theliquids settle and stratify in the lower portion of the low temperatureseparation vessel. It is necessary to supply heat to the lower portionof the vessel 22, at least at intervals, to make provision for meltingof any ice and/or gas hydrates which which may be present, and this iscarried out by the coils 25 which receive steam through the conductor 26and return condensate to the steam generator 10 through the conductor27. Through utilization of the temperature controller 29, the valve 31is opened and closed only sufficiently to maintain the desiredtemperature within the lower portion of the vessel 22, and accordingly,the very minimum amount of heat necessary for melting of the ice and/ orhydrates is employed and excessive heating of the dehydrated gas or theseparated distillates is avoided.

The separated water is removed from the sump 40 through the outletconductor 44, while the separated distillates pass from the sump 34 intothe low pressure separator 39, which is operated at a pressure wellbelow that of the vessel 22, but considerably above the pressure of thehydrocarbon storage tanks or stock tanks whereby the full benefits ofstage separation are obtained, and substantially only that gas isremoved from the distillate in the separator 39 which may not beretained in the sepa rated liquids in the storage or stock tanks. As anexample, when processing a well stream having a relatively lowhydrocarbon content, and assuming that the vessel 22 is being operatedat 1,000 pounds per square inch, along with the inclusion in the systemof the low pressure separator 39 operating at a pressure of 75 poundsper square inch at 70 R, an additional recovery of approximately onebarrel per million standard cubic feet of gas will be realized over andabove the recovery which would be made if the low pressure separator 39were not utilized. At lower operating temperatures, the increase inrecovery is,.of course, correspondingly higher. On this basis, the lowpressure separator 39 is not essential or necessarily used with theremainder of the system, but in most instances, the increased recoverywhich is realized through use of the low pressure separator warrants itsinclusion in the system. 7

Basically, the operation of the low temperature separation unitillustrated in FIG. 1 of the drawings is essentially that of the similarunits disclosed in the aforesaid US. Patent to Walker et al. No.2,747,002, with several very important exceptions. First,disregarding'those instances in which the well stream fiows at atemperature high enough to carry out the necessary heating of the lowerportion of the low temperature separator for melting of the gashydrates, the present unit may operate at lower temperatures than unitsin which the Well stream is passed through the heating coils and hencewill afford greater recoveries of marketable liquid hydrocarbons due tothe enhanced condensation of such hydrocarbons from the well stream.Assuming that the low temperature unit is operating under suchconditions of pressure that the water stratum in the lower portion ofthe separator must be maintained at a temperature of 75 to 80 F., itwill be necessary that the largely gaseous well stream leave the heatingcoils at a temperature of 90 to 100 F. due to the heat exchangeconditions between the well stream, the coils, and the liquid in thelower portion of the low temperature separator. Consequently, the wellstream will enter the choke 23 at a temperature much higher than thetemperature of gas hydrate formation, and this increased temperaturewill be reflected in the operating temperature of the low temperatureseparator 21, usually resulting in a temperature of to F. higher thancan be obtained with the present invention. Utilizing the presentdisclosure, however, the temperature of the well stream entering thechoke 23 may be maintained at a point just above the temperature of gashydrate formation, and consequently, the temperature within theseparator 21 will be depressed to the degree that will produce maximumliquefaction of hydrocarbons and maximum dehydration of the well stream.

Second, since the lowest possible temperature is achieved in theseparator 21, the gaseous portion of the well stream will be denuded ofwater and hydrocarbons to a maximum degree, thus insuring maximumdehydration and maximum removal of liquid hydrocarbons from the salesgas being withdrawn to a gas transmission pipe line through the gasoutlet conductor 32. Further, since at least a portion of the gas beingwithdrawn from the low pressure, separator 39 through the gas outletpipe 48, and on occasion, a portion of the high pressure gas withdrawnthrough the outlet 32, is utilized for fuel gas for the fire tube 11 aswell as pilot gas for operating the various controls and the motorvalves, the increased denuding of this gas of all liquids will minimizefreezing problems in the various gas supply and pilot gas lines andassure the operator of more trouble-free performance of the lowtemperature separation system.

Third, the utilization of steam coils for supplying heat to the lowerportion of the low temperature separation unit 21 takes advantage of thehigh heat transfer coefficient of steam and the high mean temperaturedifferential between the steam coil and the Warm water in the lowerportion of the vessel 22 in which the steam coil is immersed. Thispermits the low temperature separation unit 21 to accommodate largervolumes of hydrates, ice, water, and distillate due to the high heatingeffectiveness of the steam coil, and consequently, the utilization of ahigh pressure separator or water knockout upstream of the choke 23 isavoided or at least delayed for a maximum period of time. Since the unitcan handle larger volumes of liquid and hydrates, it becomes unnecessaryto remove a portion of such liquids prior to introduction of the wellstream into the low temperature separator, and thus, the expense ofinstalling, maintaining, and operating a high pressure separator orwater knockout is avoided. In addi-' tion, the unit is capable ofhandling greater quantities of drilling mud and other foreign materialwhich may be present in the well stream, along with waxes, emulsifieddistillate, and the like. Here again, the high heat transfercharacteristics of the steam coil make these additional advantagespossible. Still further, a reduction in the consumption of fuel gas isobserved since less gas must be burned to generate sufiicient steam tocarry out the desired heating functions than would be required to obtainthe same amount of heating through warm or hot gas passed through thecoils 25. This is true because all of the heat cannot be removed fromthe heated gas, whereas the steam gives up virtually all of its heat inthe form of its latent heat of vaporization, the condensate beingreturned to the steam generator 10 as a liquid very near or at theboiling point of water. Accordingly, the heat input to the steamgenerator is almost entirely utilized in the heating coils 2'5, andconsequently, a marked reduction in fuel gas consumption is obtained.

The steam generator unit '10 may be provided with all necessary ordesirable controls, the fuel gas supply line 51 having interposedtherein, as shown in FIG. 2, a motor valve 52 operated by a steampressure regulator 53, a motor valve 54 operated by a low water levelalarm 55, and such other controls and shutofi valves as may be founddesirable such as burner tube temperature shutoff valves and the like.Thus, automatic operation of the steam generator at the desiredtemperatures and pressures is ensured and the need for manualsupervision is eliminated.

As pointed out hereinbefore, the present system lends itself tointermittent operation in which the steam generator is periodicallyfired for the generation of steam to melt or thaw ice and/or gashydrates present within the low temperature separator 21 and tootherwise supply at. intervals the heating desired for continuous andproper operation of the low temperature separator. Continuous heating isnot essential, however, due to the high heating capacity of the steamsystem and the ability of such system to handle at intervals accumulatedheating requirements, possibly in the form of gas hydrates which haveaccumulated in the vessel 22 over a period of several hours. Provisionfor such intermittent heating is illustrated in FIG. 2, there beingprovided a suitable clock or time-controlled mechanism 56 driving alobed cam 57 which, in turn, operates a flapper valve 58 to open orclose an orifice 59. Supply gas under pressure is furnished to theorifice 59 through an orifice 60, and normally escapes through theorifice 59 without creating a back pressure in the branch conductor 61.When, however, one of the lobes 62 of the cam 57 engages the flappervalve 58 to close the orifice 59, a pressure will be built up in thebranch conductor '61 and communicated through the pipe 63 to the motorvalve 64, opening the latter and supplying the fuel gas to the burner 65of the fire tube 11 resulting in the generation of steam and thesupplying of heat to the coils 25.

Dependent upon the nature of the well stream being handled by the lowtemperature unit, the time-controlled, intermittent-firing mechanism maybe arranged to supply heat for one hour out of'each three or four hours,for one hour out of each eight hours of operation, or for such otherintervals and durations as may be found necessary or desirable. Withsuch an arrangement, the low temperature separator 21 will be caused tooperate at even lower temperatures than would otherwise be obtainedsince no heat would be supplied thereto for a major portion of itsperiod of operation, and further, the consumption of fuel gas by thesteam generator would be reduced to a minimum. Due to the relativelylarge internal capacity of the vessel 22, proper and eflicient lowtemperature separation may be carried out for extended periods of timewithout the supplying of any heat to the coils 25, and by reason of thehigh heating efficiency of the steam system, the vessel 22 may becompletely thawed in a relatively short time and then the supply of heatshut off so that the vessel may again operate at a minimum temperature.Of course, the lower the temperatures maintained in the vessel 22, themore complete will be the removal of liquid hydrocarbons and water fromthe gaseous well stream passing therethrough.

There may also be instances in which approximately continuous supplyingof heat to the preheater 13 is required or desirable, and in suchinstances, the intermittent heating of the low temperature separator 21may be carried out as shown in FIG. 2 by closing the valve 66 interposedin the line 63 and opening the valve 67 provided in a branch line 68leading to the motor valve 31 which is provided in the steam supplyconductor 26. In such case, the temperature controller 29 may beomitted, or it may be employed in conjunction with the illustratedintermitter structure so as to make available, through the duration ofthe heating period, upper and/ or lower limits for the temperature ofthe water stratum in the low temperature separator.

The temperature control of the incoming well stream will determine to alarge extent the internal temperature of the low temperature separatoras well as the temperature of the outgoing gas. Hence, such temperaturecontrol may be utilized for determining or varying the hydrocarboncomposition of the gas. Natural gas is, of course, predominantly methaneand includes small percentages of the higher homologues, ethane,propane, butane, isobutane, and so on up to possibly some hexane andheptane. When a rich outlet gas, possibly for processing in a gasolineplant, or a very stable distillate, or a minimum gas loss from thedischarge of distillate, is desired, the inlet well stream may bebrought to higher temperatures for production of such results.Conversely, lower inlet temperatures may be employed for producing a gasof optimum leanness or a very light distillate for subsequentprocessing, for instance, in a stabilizing column. Manifestly, dependenton the inlet stream, the composition of the outlet gas may be variedover a wide range.

Low temperature separation units are commonly operated at or near thepressure of the gas transmission pipe line into which the unitdischarges, and are also often supplied with an inlet well stream at ornear well head pressure; Of course, the pressure of the well stream maybe reduced at the well head, but because of hydrate formation and otherreasons such pressure reduction is not often carried out so that in manycases, the pres sure drop across the low temperature unit is more orless set by the well head and pipe line pressures. For this reason, thetemperature drop in the well stream is also necessarily set along withthe temperature, and therefore the general composition, of the outletgas.

By being able to vary the inlet temperature of the well streamindependently of the temperature in the bottom of the low temperatureseparator, however, the outlet temperature, and hence the composition,of the outlet gas may be controlled. Thus, by temperature control, a gasfree of butanes may be withdrawn, or a gas containing substantially allthe butanes in the well stream, within the capacity of the lowtemperature sep.. rator to make such separations. Similarly, the watercontent of the outlet gas may be controlled to a marked degree, or thepresence of other components in the gas.

A more detailed illustration of the invention is shown in FIGS. 3through 7 wherein the same numerals have been employed to identify thesame parts insofar as they substantially correspond. Necessarily, theillustration of FIG. 1 is diagrammatic in nature for purposes ofclarity, and the actual structural appearances of the various elementsvary to some degree. It is noted, however, that the structures areessentially the same and function in the same manner.

In this more detailed illustration of the invention, the steam generator10 and low temperature separator 21 are mounted upon the base or skid50, the preheater 13 being mounted on the upper surface of the steamgenerator 10. The well stream is admitted to the coil 14 of thepreheater through the inlet conductor 15 and passes therefrom throughthe conductor 16 to the choke or other pressure reducing means 23. Thereis incorporated in the conductor 16 a temperature sensing fitting 69having connected thereto a temperature controller 70 with a pilot gassupply conductor 71 leading thereto. The temperature controller 70admits and excludes pilot gas from an outlet conductor 72 leading to amotor valve 73 connected into the steam conductor 18 leading from thesteam generator 10 to the preheater 13.

For purposes of convenience, it has been found desirable to utilize afloat 74, as shown in FIG. 5, as a low water level alarm and to extendthe steam conductor 18 from the upper portion of the mounting collar 75for the float 74 to a T 76 opening downwardly through the upper side ofthe preheater 13 and upwardly to a safety relief valve 77. The float 74,of course, operates the control unit 78 which, in turn, operates theshutofl valve 54 for closing off the supply of fuel gas to the burner 65of the fire tube 11.

Returning to the temperature controller 70, by the sens ing of thetemperature of the well stream flowing to the choke 23, the controller70 may be properly set to open and close the valve 73 so as to maintainthe temperature of the well stream entering the choke 23 only slightlyabove the point of expected gas hydrate formation, and accordingly, thewell stream will be introduced into the low temperature separation unit21 at the lowest possible temperature for maximum dehydration of the gasand maximum recovery of liquid hydrocarbons. Also, the controller .70may be set to maintain the well stream temperature at a predeterminedvalue which will produce gas from the low temperature separator with apredetermined or desired hydrocarbon composition.

The utilization of a separately controlled heating coil in the lowtemperature separation unit makes possible this rather close control ofthe temperature of the incoming gas stream whereas otherwise, the wellstream might necessarily acquire a somewhat higher or lower heat contentthan desired to accomplish the selected ends. Of course, the occurrenceof gas hydrates upstream of the choke may be due to the flow of coldfrom the choke upstream through the walls of the conductor 16, or toother causes, but in any event, provision for the control of suchhydrate formation and/ or outlet gas composition has been made.

As previously described, the well stream, at minimum or a desiredtemperature, passes through the choke 23 into the interior of the unit21 and therein undergoes low temperature separation in accordance withestablished principles. Steam for heating the lower portion of the unit21 is supplied from the generator 10 through the conductor 26 and valve31 to the coil 25, any condensed steam being returned through theconductor 27 and check valve 28 to the lower portion of the steamgenerator. The temperature sensing probe 30 may, of course, bepositioned at any desired spot or location within the unit 21, it beingshown in FIGS. 3 and 4 as extending directly from the temperaturecontroller 29 through the side wall of the vessel and being operativelyconnected to the motor unit of the valve 31 through the pilot gasconductor 79.

A small liquid separator 80 is provided upon the base or skid 50 forreceiving pilot gas from a suitable source of supply and furnishing dryclean gas through the outlet conductor 81 to the manifold 82. The latterextends in turn to the supply conductor 83 for the temperaturecontroller 29, the supply conductor 84 for thedistillate level controlunit 36, the supply conductor 85 for the water level control unit 42 andthe supply conductor 86 for the control unit 45 regulating the liquidlevel control in the low pressure separator. In turn, the control unit36 has a pilot gas outlet conductor 87 leading to the motor valve 37 fordischarging distillate from the low temperature separator to the lowpressure separator, the control unit 42 is provided with a pilot gasoutlet conductor 88 extending to the water discharge valve 43, and thecontrol unit 45 has pilot gas outlet conductor 89 leading to thedistillate discharge valve 46.

The manifold 82 also extends to and is connected with the fuel gassupply conductor 51 from which fuel gas is supplied to the burner 65through the valves 52 and 54, and pilot burner fuel gas is taken offfrom the conductor 51 through the conductor 90.

As pointed out hereinbefore, the low temperature unit as illustrated inFIGS. 3, 4, and 6 is-essentially the same as the lowtemperature unitillustrated in FIG. 1 but differs in a few details in that the separatorvessel 22' is somewhat elongated and carries a heavy transverse par-'tition 91 adjacent one end portion of the vessel for enclosing the lowpressure separator 39 which, although forming a part of the vessel 22',is a separate enclosure. The distillate overflow sump 34 and wateroverflow sump 40 are. substantially the same as those previouslydescribed, the major change between the two vessels being the enclosureof the low temperature separator and the low pressure separator within asingle elongate vessel rather than the utilization of two separatevessels for carrying out the two separation steps. An inletfitting 92 isprovided in the inlet end of the low temperature separation unit, butnormally is'not employed in this system until such time that a highpressure separator or water knockout is incorporated into the systemupstream of the preheater 13. When this addition is made, the liquiddischarge conductor from the high pressure separator may desirably beconnected into the inlet fitting 92 to avoid the passage of separatedliquids through the choke 23.

A somewhat more compact form of the invention is illustrated in FIG. 8in which an elongate horizontal low temperature separation vessel 93 hasone end carried upon an upright support 94 and its opposite end carriedon the upper end of a small, low pressure vertical separator 95 having adepending base or support 96 extending downwardly to the platform orskid mounting 97 upon which the lower end of the standard 94 is alsocarried. The steam generator 98 is also mounted on the support 94 andencloses a fire tube 99 and a preheat coil 100. The generator, ofcourse, is partially filled with a volume of fresh water 101, the steamcoil 100 being disposed in the steam or vapor space of the generator,while a steam outlet 102 leads through a motor valve 103 into theheating coil 104 positioned in the lower portion of the vessel 93 abovethe steam generator and having a condensate line 105 returning to thelower portion of the generator.

The well stream inlet 106 is connected through a three-way valve 107with the inlet and outlet of the preheater coil 100 and with the wellstream conductor 108 leading to the choke 109 and diverter inletstructure 110 disposed within the upper portion of the vessel 93 andadjacent one end thereof. A gas outlet 111 is provided in the upperportion of the vessel 93, and distillate and water overflow sumps 112and 113, respectively, are provided in the opposite end of the lowtemperature vessel.

The distillate sump 112 has a drain conductor 114 leading through adiaphragm-operated or motor valve 115 to an inlet diverter 116positioned interiorly of the low pressure separator 95, while the wateroverflow sump 113 has a water outlet conductor 117 leading through amotel valve 118 to a suitable point of water disposal. The low pressureseparator has a gas discharge conductor 119 extending through a backpressure valve 120, and a hydrocarbon or distillate discharge conductor121 through which flow is controlled by a motor valve 122.

The three-way valve 107 is operated by a temperature controller 123arranged to respond to the temperature of 1 the fluid passing throughthe conductor 108 and to shift the valve 167 so as to pass a portion orall of the well stream through the preheater coil 100, or to exclude thewell stream from such coil, in order to maintain the well stream at theinlet to the choke 109 at a temperature only slightly above the point ofexpected gas hydrate formation or at a temperature which will controlhydrate formation and/or outlet gas composition. Similarly, the valve103 is operated by a temperature controller 124 which responds to atemperature probe 125 positioned in the water stratum in the lowerportion of the vessel 93 and functioning to maintain said water stratumat a desired or predetermined temperature which will control hydrates inthe vessel 93. The distillate overflow sump 112 receives a float 126which operates a pilot valve or controller 127 which, in turn, operatesthe valve 115 to drain distillate from the sump into the low pressuresepara-tor 95 in accordance with its rate of accumulation.

Similarly, the sump 113 receives a float 128 operating a controller 129for opening and closing the valve 118 and discharging water from thewater overflow sump. A float 130 is positioned within the low pressureseparator 95 for operating a pilot valve 131 and, in turn, operating thevalve 122 for discharge of separated distillate from the low pressureseparator to storage tanks or other point of disposition.

In some instances, it may be desirable or necessary to provide means forheating the choke, or other expansion means as employed in the variousforms of the invention, and such means is illustrated in FIG. 8 of thedrawings in which the choke 109 is partially or completely enclosed bythe steam jacket 132 having a steam supply conductor 13-3 extendingthereto from the lower portion of the supply conductor 102. A condensatereturn conductor 134 leads from the jacket 132 to the condensate returnconductor 10-5.

For regulating the heating of the choke, a control valve 135 is insertedin the conductor 133 and operated by a temperature controller 136 havinga temperature sensing probe 137 responsive to the temperature in thejacket 132 or to the temperature of the walls of the choke 109. Hereagain, a single source of heating medium, such as the steam generator,is employed for supplying heating under separately and independentlycontrolled conditions to a particular element in the low temperatureseparation system which may require such heating. The heating of thechoke is readily carried out from the same source of heating medium butis controlled entirely separately from the preheating of the well streamas well as separately from the heating of the lower portion of the lowtemperature separation vessel.

In all principal respects, this last described form of the inventionpossesses all of the advantages and benefits, and operates insubstantially the same manner as the previously described forms, butincludes the additional advantages of an extremely compact structure.Further, the separate preheater, enclosure is eliminated and the vaporspace of the low pressure steam generator is utilized for reception ofthe preheater coil 100.

It is manifest that all forms of the invention may be modified toreceive the intermittent heating controller illustrated in FIG. 2, itbeing noted in each instance that thecontroller may either open andclose a motor valve controlling the supply of fuel gas to the fire tubeburner, or may operate separately in conjunction with the temperaturecontroller 29 or 124 for controlling steam supply to the heating coils25 or 104 so that separate control of the preheater coil in its degreeof heating of the incoming well stream may be carried out as foundnecessary or desirable. In all respects, each form of the inventionprovides for operation of the low temperature separation unit at minimumtemperatures to provide maximum dehydration of the well stream andmaximum recovery of marketable liquid hydrocarbons, the preheater coilmaking provisions for well streams which tend to form gas hydrates.prior to entry into the choke or other pressure reducing element, whilethe low pressure separator may be included for further stabilization ofthe recovered distillate and greater recoveries of such distillate.

Further, each form of the invention provides for operation of the lowtemperature separation unit at a temperature which will produce adesired hydrocarbon composition for the dehydrated gas and will controlhydrate formation prior to entry of the well stream into the choke orother pressure-reducing means.

It is further noted that any or all of the vessels or enclosures formingcomponents of this system may be of either the horizontal or verticaltype. It is also to be noted that in each modification of the invention,the heating coils in the low temperature separator are at an elevationabove the steam generator, or at least above the water level in thegenerator. Hence, the coils are always maintained free of water, and inthe event of burner failure or prolonged shutting down of the burnerdue, for instance, to a low water level, possible freezing and rupturingof the heating coils within the relatively high pressure enclosure ofthe low temperature separator is avoided. Although of less consequence,the preheater is also above the steam generator in some of the forms ofthe invention.

In some cases, other heating mediums than steam may be employed such asglycols, oils, hi h boiling point organic heat exchange materials, andthe like.

The foregoing description of the invention is explanatory thereof andvarious changes in the size, shape and materials, as well as in thedetails ofv the illustrated construction may be made, within the scopeof the appended claims, without departing from the spirit of theinvention.

What we claim and desire to secure by Letters Patent is:

l. The method of low temperature separation of high pressurepredominantly gaseous well streams including, chilling the well streamby passing the stream through a pressure reduction step and into a lowtemperature separation zone wherein the well stream separates andstratifies into a gaseous stratum and cold water and hydrocarbon strata,withdrawing gas from the separation zone, withdrawing water andhydrocarbons from the separation zone, intermittently heating at leastthe water stratum for periods of time of shorter duration, andterminating said heating for periods of time of longer durationalternately with said periods of heating.

2. The method of low temperature separation of high pressurepredominantly gaseous well streams including, chilling the well streamby passing the stream through a pressure reduction step and into a lowtemperature separation zone wherein the well stream separates andstratifies into a gaseous stratum and cold water and hydrocarbon strata,withdrawing gas from the separation zone, withdrawing water andhydrocarbons from the separation zone, intermittently heating at leastthe water stratum with steam for periods of time of shorter duration,and terminating said heating for periods of time of longer durationalternately with said periods of heating.

3. The method of low temperature separation of high pressurepredominantly gaseous well streams including, chilling the well streamby passing the stream through a pressure reduction step and into a lowtemperature separation zone wherein the well stream separates andstratifies into a gaseous stratum and cold water and hydrocarbon strata,withdrawing gas from the separation zone, withdrawing water andhydrocarbons from the separation zone, heating at least. the waterstratum at timed intervals 12 for periods of time of short duration, andterminating said heating for periods of time of longer durationalternately with said periods of heating to cause the water stratum tochill to a maximum degree to cause maximum liquefaction of hydrocarbonsfrom the well stream.

4. The method of low temperature separation of high pressurepredominantly gaseous well streams including, chilling the well streamby passing the stream through a pressure reduction step and into a lowtemperature separation zone wherein the well stream separates andstratiiies into a gaseous stratum and cold water and hydrocarbon strata,withdrawing gas from the separation zone, withdrawing waterandhydrocarbons from the separation zone, and intermittently heating atleast the water stratum with steam while continuously withdrawing allcondensed steam in the form of water from the water stratum heatingzone.

5. The method of low temperature separation of high pressurepredominantly gaseous well streams including, preheating the well streamwith a first portion of heating medium from a single source of heatingmedium, chilling the well stream by passing the stream through apressure reduction step and into a low temperature separation zonewherein the well stream separates and stratifies into a gaseous stratumand cold water and hydrocarbon strata, withdrawing gas from theseparation zone, withdrawing water and hydrocarbons from the separationzone, heating at least the water stratum with a second portion ofheating medium from the single source of heating medium for timedintervals, terminating said heating of the water stratum for periods oftime alternately with said intervals of heating for bringing thetemperature of the water stratum down to a level to cause maximumliquefaction of hydrocarbons from the well stream, and separately andindependently controlling the supplying of the heating medium to thepreheating and heating steps.

6. The method of claim 5 in which the supplying of the heating medium tothe preheating step is controlled to produce gas from the separationzone having a predetermined level of hydrocarbons heavier than methane.

7. A low temperature separation system for high pressure predominantlygaseous well streams including, a hot fluid generator, a low temperatureseparator, a well stream inlet conductor to the separator, means in theinlet conductor for causing the well stream to undergo a pressurereduction to chill the well stream, a gas outlet from the separator,means for withdrawing water and hydrocarbons from the separator, hotfluid heated means in the separator for heating the lower portion of theseparator, and means for supplying hot fluid from the generator to thehot fluid heated means at spaced intervals of time.

8. A low temperature separation system for high pressure predominantlygaseous well streams including, a low pressure steam generator, a lowtemperature separator, a well stream inlet conductor to the separator,means in the inlet conductor for causing the well stream to undergo apressure reduction to chill the well stream, a gas outlet from theseparator, means for withdrawing water and hydrocarbons from theseparator, steam heated means in the separator for heating the lowerportion of the sepa' rator, and means for supplying steam from thegenerator to the steam heated means at intervals spaced apart bypredetermined periods of time.

9. A low temperature separation system for high pressure predominantlygaseous well streams including, a low pressure steam generator adaptedto contain a body of water at a predetermined level, a low temperatureseparator, a well stream inlet conductor to the separator, means in theinlet conductor for causing the well stream to undergo a pressurereduction to chill the well stream, a gas outlet from the separator,means for withdrawing water and hydrocarbons from the separator, steamconducting means for heating the lower portion of the separator, said.steam-conducting means being disposed at an 13 elevation above thepredetermined water level in the generator, and means for supplyingsteam from the generator to the steam-conducting means.

10. A low temperature separation system for high pressure predominantlygaseous Well streams including, a stream generator, a preheater, a lowtemperature separator, a well stream inlet conductor extending throughthe preheater to the separator, means in the inlet conductor for causingthe well stream to undergo a pressure reduction to chill the Wellstream, a gas outlet from the separator, means for withdrawing water andhydrocarbons from the separator, steam-conducting means for heating thelower portion of the separator, means for supplying steam from thegenerator to the preheater and the steam-conducting means, means forindependently controlling the supplying of steam to the preheater, andmeans for independently supplying steam from the generator to thesteam-conducting means at spaced intervals of time.

11. A low temperature separation system for high pres sure predominantlygaseous Well streams including, a steam generator, a low temperatureseparator, a well stream inlet conductor to the separator, means in theinlet conductor for causing the Well stream to undergo a pressurereduction to chill the well steam, at gas outlet from the separator,means for withdrawing water and hydrocarbons from the separator, steamheated means in the separator for heating the lower portion of theseparator, and means for maintaining the low temperature separator atsuch low temperature as will atiord maximum liquefaction of liquids fromthe well stream by supplying steam from the generator to the steamheated means at spaced intervals of time.

References Cited in the file of this patent UNITED STATES PATENTS OTHERREFERENCES Petroleum Refiner, vol. 32, No. 1, January 1953, pages138-142.

